Electro-pneumatic converter

ABSTRACT

An electro-pneumatic converter device with modular components and with supporting housing structure enabling the device to be readily convertible from a current to pressure positioner to a current to pressure transducer. A valve positioner with an enclosure having a housing, a modular base, and a separable field terminal box. A self contained cover mounted to the enclosure with no additional mounting components. A plastic pneumatic relay ultrasonically welded together to eliminate metal mounting parts and lower assembly time. Open channels in a housing surface cooperating with a gasket to provide fluid passageways between the housing and the modular base. Pressure gauges are removably mounted on a modular unit for location completely within the housing. A floating interconnect terminal board permits self-aligning of mating terminals as the modular unit is inserted into the housing. A supply biased pneumatic pressure relay has supply pressure channeled to the supply port and also to a supply bias cavity through a capillary hole.

This is a continuation-in-part of application Ser. No. 07/942,758, filedSep. 9, 1992, now abandoned.

This invention relates to electro-pneumatic converter devices and inparticular to current to pressure transducer/positioner devices.

BACKGROUND OF THE INVENTION

Electro-pneumatic converters, such as current to pressure transducersare in common use as field instruments mounted in pipeline systems forcontrolling the process fluid. Subsequently these devices are installedin potentially hazardous explosive environments. Such devices receive,for example, a variable current input signal of between 4-20 mA andeventually provide a variable pressure output to an actuator for a fluidcontrol valve. Since these devices can be employed in a potentiallyexplosive environment, to provide an explosion proof device theelectrical and pneumatic components are isolated within an explosionproof portion of the transducer/positioner unit, except for the pressuregauges which are normally located on the unit exterior.

With presently available electro-pneumatic converters operating in apotentially explosively hazardous area, in the event either service ofthe unit or normal maintenance is required, the electric power must bedisconnected and/or the entire unit must be removed from the potentiallyhazardous area in order to be worked on. Occasionally, for instance, thepneumatic elements must be adjusted or removed and replaced. In presentunits, if the seal of the explosion proof portion of the unit is removedin order to get access to these pneumatic elements, then a potentiallyunsafe condition is created where any spark caused in the electricalelements could ignite potentially explosive gases. Accordingly, shuttingdown the electrical power in order to service or remove the unit fromthe hazardous area is time consuming, costly, and wasteful.

In addition, with the electrical and pneumatic components maintainedwithin an explosion proof portion of the transducer/positioner unit, themounting of the pressure gauges on the portion outside the explosionproof portion of the unit is required. However, this exposes thepressure gauges to the atmosphere as well as to physical damage fromunintentional blows to the pressure gauges protruding even slightly fromthe transducer/positioner exterior surface.

Accordingly, it is desired to provide an electro-pneumatic converterwhich can be used in a potentially explosive environment and whereinpneumatic components can be serviced without requiring electricalshutdown or removal of the entire unit from the hazardous area.

In addition, it is desired to provide an electro-pneumatic converterwhere the pressure gauges can be protected from the atmosphere as wellas from any unintentional physical damage.

Currently available pressure transducer instruments contain a pressureto current sensor to convert a pressure signal to a current signal insupplying feedback to the instrument. Analog pressure transducer unitsare available, as well as respective digital pressure transducer units.Also currently available are separate valve positioner units whichincorporate feedback from the valve supplied from a mechanical linkagewith the valve stem. Both analog valve positioner units and digitalvalve controller units are separately available.

Typically, the customer chooses the type of instrument needed in orderto fit within his present system. Thus, a customer may initially chooseto purchase a pressure transducer instrument in analog form as mostconveniently adaptable to his present system. If the customer's systemchanges or he wishes to modify his system to operate in digital form,the customer must then purchase the required separate instruments. Also,if the customer wants to change to a valve positioner configuration whenhe initially purchased a pressure transducer instrument, he mustpurchase a new valve positioner device in the proper data format to fithis changed system.

It is therefore further desired to provide an electro-pneumaticinstrument which is usable and readily convertible from a pressuretransducer to a valve positioner or vice versa. In addition, it isdesired to enable a user to readily convert from an analog data handlingcapability to a digital data handling capability or vice versa.Furthermore, it is desired to enable the instrument user to incorporateand to change to any desired communications data protocol.

In existing electro-pneumatic instruments, the instrument housing isusually formed of a casting. The casting must then be drilled withprecise holes to form passageways and interconnected passageways toenable the desired communication of fluid between components. Forming ofthe desired passageways by drilling intersecting holes in the castingrequires time consuming precision drilling and set up of the housingsfor drilling. Present instruments also utilize many individualsub-assembly components requiring stocking and assembly time. Theinstrument covers, for instance, normally require two or more pins andlocks or other multi-part fasteners to mount the cover to theinstrument. This requires an inventory of the several parts and aninordinate amount of assembly time to assemble the cover to theinstrument.

Pneumatic relays, used extensively in positioners and transducers,normally have been made from aluminum based materials. Machine screwsare used to assemble the aluminum relay body components together whileclamping rubber diaphragms and O-rings to provide the pressure seals.Assembly of these numerous subassembly components of present pneumaticrelays is tedious and costly in the manufacturing environment.

It is desired therefore to eliminate components or at least reduce thenumber of components required for an electro-pneumatic instrument.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a versatilemodular configuration for an electro-pneumatic instrument that can serveas a platform of construction for a wide range of output devices whichincludes, for example: a digital pressure transducer; a digital valvecontroller; an analog valve positioner; and an analog pressuretransducer. All of the aforementioned output devices available from thepresent invention can provide the following features:

1. A modular configuration with a field termination compartment, anelectronics compartment, and a pneumatic compartment which are allenvironmentally segregated from each other;

2. A modular configuration which is explosion proof, and allowsmaintenance and service-ability of the pneumatic elements withoutinterfering with the electrical components; and

3. A modular configuration permitting user selected variations infeedback and mountings to accommodate both sliding stem valve actuatorsand rotary shaft valve actuators.

In accordance with the principles of the present invention, there isprovided an electro-pneumatic instrument of modular construction whichis readily convertible from a pressure transducer to a valve positionerand vice versa. In the preferred embodiment of the invention, theconvertible instrument includes an enclosure having a housing defining ahollow interior, and a modular base containing electrical and pneumaticcomponents, where the modular base is removably insertable into thehousing. A housing portion is included on the housing and is adapted forreceiving and mounting therein a potentiometer and shaft in convertingthe instrument to a valve positioner. The housing portion communicateswith the hollow interior to enable the potentiometer output to beconnected to the electrical components on the modular base via thehousing portion and the housing hollow interior.

The housing portion may be formed of an elongated cylindrical bossextending along the housing and which includes a pocket interior toreceive the potentiometer at one end. The pocket interior intersectswith the housing hollow interior and a bushing is threadably mounted onthe elongated cylindrical boss to supportably mount the potentiometershaft.

In converting a valve positioner utilizing the present electro-pneumaticinstrument of the present invention to a pressure transducer, this canbe readily provided by removing the potentiometer from the housingportion, disconnecting the potentiometer output cable from the mainprinted circuit board mounted on the modular base, and replacing themain circuit board to accommodate the signals appropriate to a pressuretransducer as is known in the art.

The preferred embodiment also includes an electrical terminal boxmounted on the housing with a passageway between the housing interiorand the terminal box. An electrical terminal board is replaceablymounted in the terminal box which includes a removable cover for accessthereto. A cable harness is connected to the electrical terminal boardin the terminal box and extends through the passageway and the housinghollow interior for connection to the main circuit board on the modularbase. The terminal board and cable harness are replaceable toaccommodate corresponding desired formats and functions, such as analog,digital, communication or data protocols.

In accordance with another aspect of the present invention, a housing isprovided with a substantially flat housing mounting surface with openchannels or slots within the surface. A modular base has a modular basemounting surface opposite to the housing mounting surface. A gasket isprovided intermediate the housing mounting surface and the modular basemounting surface. The gasket covers the open channels so as to definethe housing fluid passageways, and further includes apertures forcommunicating the housing fluid passageways to the modular base fluidpassageways. A distinct advantage of this aspect of the invention is theelimination of the need to drill precise holes through the housing or toprecisely locate and drill intersecting holes to form the desired fluidcommunicating passageways.

In accordance with still another aspect of the present invention, thereis provided a cover with self-contained mounting ears shaped for ease ofinserting the ears into the module base so the cover is retained on themodule base in a closed configuration and yet can be readily removedfrom the module base if desired in an open configuration.

In accordance with a further aspect of the present invention, there isprovided a pneumatic relay with plastic molded structural bodycomponents. These components are ultrasonically welded together in amanner that clamps the diaphragm to provide the pressure seals, thuseliminating the need for machine screws. Thus, the number ofsub-assembly components are minimized and the assembly costs for thepneumatic relay are drastically reduced by almost one-half.

There is also provided an electro-pneumatic converter in the form of acurrent to pressure transducer/positioner unit having an enclosure whichincludes a housing and module base for electrical and pneumaticcomponents with a compartmented portion of the unit forming twosegregated compartments for the respective electrical and pneumaticcomponents. A dividing interior wall between opposite sides of themodule base defines a segregated compartment between the dividinginterior wall and a first portion of the module base opposite thedividing interior wall in a first direction. This segregated compartmentpreferably contains the electrical components. Another segregatedcompartment is defined between the dividing interior wall and a secondportion of the module base opposite the dividing interior wall in asecond direction opposite from the first direction for preferablycontaining the pneumatic components isolated from the electricalcomponents.

A removable cover is preferably provided for the segregated compartmentcontaining the pneumatic components. Accordingly, removing the coverenables access to the pneumatic component segregated compartment forservicing the pneumatic components while maintaining the electricalcomponents isolated. Therefore, with the present invention, theexplosion proof electronic compartment remains isolated and undisturbedand all of the explosion proof elements can remain intact while oneservices the pneumatic elements in the unit of the present invention.Thus, there is no need to disconnect the electrical power while workingon the pneumatic elements in the unit of the present invention.

The significant advantage of this aspect of the invention includes theability to adjust or remove and replace the pneumatic elements while thepower is connected without breaking the seal of the explosion proofportion of the transducer/positioner. Other significant advantagesinclude the ability to provide additional maintenance features, such asstroking the pneumatic elements fully opened or closed to performmaintenance diagnosis of the unit. The pneumatic elements can also beadjusted to change pneumatic zero during maintenance or troubleshooting.Also, access to the supply pressure primary restriction which may becomecome clogged and requires cleanout is readily provided in accordancewith this invention.

In accordance with another aspect of the present invention, anelectro-pneumatic converter unit includes an enclosure having a housingdefining a hollow interior and a modular base removably insertable intothe housing hollow interior so as to be surrounded by the enclosure.Electrical and pneumatic converter components are mounted on the modularbase including one or more pressure gauges so that the pressure gaugesare located within the enclosure and thereby protected from theenvironment and any physical damage. The gauges, which are mounted inthe pneumatic compartment are in an atmosphere which is constantly beingpurged by the supply pressure medium, thus affording them additionalprotection to corrosive atmospheres not seen with devices withexternally mounted pressure gauges. The pressure gauges are preferablythreadably mounted on the modular base for ease in servicing andreplacement.

In accordance with still another aspect of the present invention, themodular base includes a dividing interior wall. First means are providedfor mounting the electrical components on one side of the dividinginterior wall. Second means are provided for mounting the pneumaticcomponents including pressure gauges on the opposite side of thedividing interior wall. Accordingly, as the modular base is insertablymounted into the housing interior, segregated compartments are definedfor respectively isolating the electrical components from the pneumaticcomponents.

In accordance with still another aspect of the invention there isprovided an improved pneumatic pressure relay for a fluid actuatorcontrol valve assembly. The supply pressure is communicated to a supplybias cavity through a capillary hole to maintain a substantiallyconstant supply pressure of the relay. Pressure transients in responseto load changes are isolated from the supply bias cavity by thecapillary hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of this invention which are believed to be novel are setforth with particularity in the appended claims. The invention may bebest understood by reference to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals identify like elements in the several figures and in which:

FIG. 1 is a front elevational view illustrating a current to pressuretransducer having an enclosure with a housing and a removable modulebase in accordance with the present invention;

FIG. 2 is a cross-sectional view taken along section lines 2--2 of thecurrent to pressure transducer shown in FIG. 1, with certain componentsremoved for clarity;

FIG. 3 is a sectional view of the module taken along section lines 3--3of the current to pressure transducer shown in FIG. 1, with certaincomponents removed for clarity;

FIG. 4 is a sectional view taken along section lines 4--4 of the currentto pressure transducer shown in FIG. 2, with certain components removedfor clarity;

FIG. 4A is a fragmentary sectional view taken along section lines 4A--4Aof the current to pressure transducer shown in FIG. 1;

FIG. 5 is a fragmented sectional view taken along section lines 5--5 ofthe current to pressure transducer shown in FIG. 1, with certaincomponents removed for clarity;

FIG. 6 is an elevational view showing an interconnect board forconnecting electrical terminals;

FIG. 7 is an elevational view showing the interior of the housing withthe interconnect board floatably mounted therein;

FIG. 8 is a schematic sectional view showing a shoulder screw mountingthe interconnect board in a floating manner;

FIG. 9 is a sectional view showing a supply biased pneumatic pressurerelay;

FIG. 10 is a perspective view of a preferred embodiment of the inventionillustrating a valve positioner in modular configuration which can bereadily converted to a pressure transducer;

FIG. 11 is a sectional view of the preferred embodiment of the inventiontaken along section lines 11--11 of the valve positioner shown in FIG.10;

FIGS. 12 and 12A are exploded perspective views of the modularconfigured valve positioner of FIG. 10, the two figures beingconsecutively locatable along the same central reference axis along thedirection indicated by the respective arrowheads;

FIG. 13 is an elevational view showing a modular base with somecomponents removed for clarity;

FIG. 14 is a sectional view taken along section lines 14--14 of themodular base shown in FIG. 13;

FIG. 15 is a fragmented view partly in section showing a pressure sensorsensing the output pressure;

FIG. 16 is an elevational view of the instrument housing portion showingchannels in the surface for fluid passageways;

FIG. 17 is an elevational view of the modular base showing the modularbase surface facing the housing surface of FIG. 16; and

FIG. 18 is a schematic block diagram illustrating the electro-pneumaticconverter instrument readily convertible from a valve positioner to apressure transducer and vice versa.

DETAILED DESCRIPTION

The modular and convertible aspect of the invention illustrated in FIGS.1-9 will be described in connection with an embodiment comprising acurrent to pressure transducer. It is to be understood that theteachings herein can as well be applied to other electro-pneumaticconverter devices to solve problems similar to those which are solved bythe present invention. As an example, while this description is inconnection with a current to pressure transducer, it is well-known inthe art that such devices can readily be converted to a current topressure positioner following the teachings herein.

The flexible modular and convertible aspect of the invention illustratedin FIGS. 10-18 will be described in connection with a preferredembodiment comprising a current to pressure positioner which is morereadily convertible to a current to pressure transducer and vice versathan the embodiment of FIGS. 1-9. Accordingly, the present descriptionis to be understood to be for purposes of describing the preferredembodiment and is not meant to limit the scope of the invention and theclaims. Thus, the invention and the claims are to be given a broadinterpretation consistent with the teachings herein.

I. Convertible Current To Pressure Transducer

Referring now to FIGS. 1 and 2, there is illustrated a current topressure transducer 10 having an enclosure which includes a housing 12with one portion defining a hollow interior 14. The housing 12 includesa field terminal box portion 16 including a field terminal strip 18 forsuitable connection to an electrical signal cable for receiving acurrent control signal from a distributing control system, so as to forinstance monitor a process. End cap 20 is removable from the housing sothat the appropriate cable wiring connections can be made to terminal18.

Housing 12 also includes an inlet 22 for receiving a supply pressurefrom a pneumatic supply source, and an outlet port 24 through which theoutput pressure can be suitably coupled to a positioner or directly to avalve actuator. Typically, in response to a variable 4-20 mA currentcontrol signal, current to pressure transducer 10 provides a variablepressure output at outlet 24.

A modular base 26 (see FIG. 3) contains the electrical components andthe pneumatic components for current to pressure transducer 10.Typically, this will consist of a current to pressure converter devicesuch as a I/P nozzle block having a flapper for converting the variablecurrent control signal input into a variable nozzle pressure signal; apressure relay receiving the variable nozzle pressure signal andproviding a variable pressure output on outlet 24; a pressure gaugemonitoring the supply pressure coupled to inlet port 22; a secondpressure gauge monitoring the pressure output on outlet 24; andelectronic equipment such as a pressure sensor and a printed circuitboard with circuitry to process the electrical signals as required.

Modular base 26 includes a metal base 28 having a threaded ring 30 andO-rings 32 so that modular base 26 can be inserted into housing 12 bythreadable engagement. Reference may be made to FIG. 2, wherein modularbase 26 is shown in its complete threadable mounting position when fullyinserted within housing 12.

The modular base also includes a modular wall 34 which provides themounting of the pressure components on one side and the electricalcomponents on the other side. In the modular base 26, and opposite wall34, there is provided a masking plate 36 and a clear cover plate 38forming a pressure compartment 40 in the modular base and definedbetween modular wall 34 and cover plate 38. With reference to FIG. 2, itcan be seen that when the modular base is insertably mounted into thehousing, an electrical compartment 42 is defined as part of housinginterior 14 and is specifically defined between modular wall 34 and ahousing side 44.

With reference to FIGS. 1-3 it can be seen that the pressure componentsare mounted in the modular base on one side of modular wall 34 and theelectrical components are mounted on the other side of wall 34. Forexample, an I/P nozzle block-flapper unit 46, a pneumatic relay 48, andpressure gauges 50, 52 are all mounted in pneumatic compartment 40 onone side of wall 34. A printed circuit board 54 containing electricalcomponents and a pressure sensor 56 are mounted on the opposite side ofmodular wall 34 so that they are confined within electrical compartment42 when the modular base is inserted into the housing.

Accordingly, as can be seen from FIG. 2, the electronic components areisolated within segregated electrical compartment 42 and the pressurecomponents are isolated in segregated pressure compartment 40 onopposite sides of modular wall 34. All of the electrical and pneumaticcomponents, including the pressure gauges, are maintained within theinstrument enclosure. It is understood, of course, that suitableexplosion preventing devices are inserted in the orifices through wall34 which may otherwise interconnect compartments 40 and 42. As anexample, with reference to FIG. 3, aperture 58 through wall 34interconnects pressure gauge 52 and pressure sensor 56. A commerciallyavailable item known as a flame arrester 60 is inserted in aperture 58.The flame arrester 60 may comprise a porous metal plug which allowspressure to pass through the plug but which will cool and lower thetemperature of any flame in aperture 58 to prevent ignition ofpotentially hazardous environments.

Threaded ring 30 is free to rotate with respect to metal base 28. Thethreaded ring is securely captured between metal base 28 on one side andtwo stanchions 62 mounted to metal base 28 and having a projecting ledge64 slightly spaced from a rim 66 of threaded ring 30.

This enables the threaded ring to rotate and threadably engage athreaded housing portion 68 so as to securely mount and seal the metalbase 28 through O-rings 32 with respect to housing 12.

In accordance with one aspect of the present invention, it may be notedthat while the pressure components and the electrical components havebeen isolated within the enclosure formed by housing 12 and modular base26 to prevent any inadvertent spark from the electrical components toignite potentially hazardous environments which may be present in thepressure components, yet the pressure components can be serviced andmaintained without shutting down the power or requiring removal of unit10 from the potentially hazardous area. With respect to this aspect ofthe present invention, note that removal of cover 38 and mask 36 fromthe enclosure provides access to the pressure components within pressurecompartment 40 while still maintaining the isolation of the electricalcomponents in electrical compartment 42.

Thus, the I/P nozzle block 46 can be serviced without turning off theelectrical power. For instance, the pneumatic elements can be adjustedto pneumatic zero during maintenance or troubleshooting by affordingaccess to a zero adjustment nut 70 on the I/P nozzle block unit. Also,access is permitted to a cleanout wire 72 to permit the wire to be usedto cleanup the pneumatic restriction or orifice in the air supply linewhich can become clogged. In a similar manner, the pressure gauges canbe threadably removed from the module and replaced, if necessary,without shutting off the power supply. Servicing of the pneumatic relaycan also be performed with the complete isolation of the electricalcomponents in electrical compartment 42.

In accordance with another aspect of the present invention, it may benoted that pressure gauges 50 and 52 are mounted totally within theenclosure formed by housing 12 and modular base 26 so they are notsubject to the environment or to any physical damage from actionsoutside of the housing. Yet, the pressure gauges can be removed or aresubject to repair by removing replaceable cover 38 and mask 36 toprovide access to pressure compartment 40.

FIG. 4 illustrates the modular wall 34 which contains a longitudinalpassageway to communicate the inlet pneumatic supply at an inlet end 76into I/P nozzle block 46 and to communicate the I/P nozzle blockvariable pressure output into the pneumatic relay 48. Referring now toFIG. 4A, there is illustrated modular wall 34 and the passagewaysthrough the modular base for connecting the supply pressure from inletend 76 to passageways 77 and 79 to the I/P nozzle block 46 from the mainsupply passage 81. The variable pressure output of nozzle block 46 issupplied through a passageway 83 to interconnecting passageway 74 to thepneumatic relay 48.

With reference to FIG. 3, it can be seen that passageway 81 connects toa transverse passageway 85 at the inlet end 76 for eventualcommunication with inlet port 22 for receiving the pneumatic supplypressure when the modular unit is mounted in the housing.

With reference to FIG. 4, apertures 78 are shown in the modular wall topermit the electrical connections from printed circuit board 54 throughthe modular wall to the I/P nozzle block. As indicated previously, theseapertures also contain suitable explosion proof seals to isolate andprevent any sparks in electrical compartment 42 from causing ignition ofpotentially hazardous environment through the wall 34 and into pressurecompartment 40.

In accordance with another aspect of the present invention, the matingof connections between the housing terminals and the modular terminalsis provided by a blind connection, i.e. automatically as modular base 26is insertably mounted into housing 12. The electronic components onprinted circuit board 54 are electrically connected to a modularterminal strip 80 containing modular terminals 82, which as shown inFIG. 5 consist of a plurality of male terminal pins. Printed circuitboard 54 is mounted within a plastic cover 84, preferably by epoxymolding of all of the units within the plastic cover. Cover 84 is inturn mounted to modular wall 34 through the use of appropriate threadedscrews 86. As shown in FIG. 5, modular terminals 82 protrude throughcover 84 for engagement with female housing terminals 88 contained on ahousing terminal strip 90 which in turn is mounted to a housinginterconnect board 92.

With reference to FIGS. 6 and 7, there is indicated the manner in whichthe housing interconnect board is floatably mounted so as to permitself-aligning of the board with the modular terminal pins. Housing side44 includes a pair of upright ribs 94 each having a threaded aperturefor receiving a respective mounting screw 96. Preferably, mountingscrews 96 are shoulder screws so that the bottom of the shoulder buttsagainst the rib and prevents further penetration of the shoulder screwinto the threaded aperture of the rib.

Referring to the schematic illustration of FIG. 8, this configuration isillustrated in more detail. Threaded aperture 98 within rib 94 receivesa threaded portion 100 of screw 96 until a shoulder 102 compressinglyabuts against rib 94. As seen in FIG. 8, the length of shoulder 102 isgreater in dimension than the width of housing interconnect board 92.Therefore, the housing interconnect board can float longitudinally alongscrew 96 and between the screw head and the top of rib 94. If desired,screw head 96 can be sized for this purpose or, a larger washer 106 maybe utilized. In addition, apertures 104 in housing interconnect board 92are made slightly larger in diameter than the diameter of shoulder 102.This permits the interconnect board to slightly move transversally withrespect to the screw. Thus, housing interconnect board is securelycaptured by screw 96 and ribs 94 but is allowed to float in positionbetween the screw and the rib so that the housing terminals areself-aligned with the modular terminals during the insertable mountingof modular base 26 into the housing.

To guide the modular terminals in the correct orientation with respectto the housing terminals, a longitudinal groove 108 is provided on theinside surface of the housing. Groove 108 matches an indexing pin 110which is fixed within the outer surface of metal base 28. Thus, ininserting modular base 26 into the housing, the modular base is rotateduntil indexing pin 110 is fitted within longitudinal groove 108 tocorrectly position modular terminals 82 with the housing terminals 88.Thereafter, as threaded ring 30 is rotated to move the modular base intothe housing, because of the floating mounting of housing interconnectboard 92, the female housing terminals 88 become self-aligned with themale modular terminals 82 to achieve the final electricalinterconnection of the modular base with the housing interconnect boardas shown in FIG. 5.

A flexible electrical cable 112 interconnects the housing interconnectboard 92 with a small printed circuit board 114 which in turn isconnected to a series of RFI filters 116 with the filters 116 connectedthrough housing 12 to appropriate field terminals 18.

Since the transducer unit can readily be converted to a positioner asknown in the art, housing interconnect board 92 also includes suitableconnections 118 for connection to a potentiometer. For a transducerunit, a plug 120 is threadably mounted into housing side 44 to close offelectrical compartment 42. When the unit is to be used as a positioner,a potentiometer can be mounted in the electrical compartment forelectrical connection to connectors 118 and with the potentiometer shaftextending through an aperture with suitable flame arresting devices in aplug.

Referring now to FIG. 9, there is illustrated an improved pneumaticpressure relay 48 which receives a variable control pressure on inlet122 and delivers a variable output pressure on outlet 124 coupled topneumatic outlet 24 of housing 12 (see FIG. 1) for communication with avalve actuator. Relay 48 also includes a supply pressure inlet 126coupled to the inlet 22 of housing 12 (see FIG. 1) for connection to asource of pneumatic supply pressure. Relay 48 also includes an exhaustoutlet 128.

Pneumatic pressure relay 48 includes a supply bias portion forestablishing the start point of the pneumatic pressure input range atinlet 122 for a given supply pressure at inlet 126. The start pointinput pressure will change with changing supply pressures and thereforeallows the relay 48 to operate at different supply pressures withouthardware changes, such as bias springs. With reference to FIG. 9, it maybe seen that relay 48 includes an input signal diaphragm 130, an inputsupply port 132, and an exhaust port 134. The movement of diaphragm 130in response to the variable pressure input on inlet 122 controls theopening and closing of the input supply and exhaust ports. A valve rod136 includes a supply valve plug 138 at one end and an exhaust valveplug 140 at the other end.

A valve spring 142 seated against plug 138 and cap 144 normallymaintains plug 138 seated against input supply port 132 as shown in FIG.9. This blocks the supply pressure from inlet 126 from reaching theactuator outlet 124 which supply pressure otherwise would communicatethrough passageways 146, 148, through an open input supply port 132 andthrough a passageway 150 to actuator outlet 124.

The drive coupling between input signal diaphragm 130 and valve rod 136is provided through three intermediate diaphragm mounting bodies, namelyan upper body 152, a middle body 154 and a lower body 156. An uppersupply bias diaphragm 158 is captured between bodies 152, 154 and alower supply bias diaphragm 160 is captured between middle block 154 andlower block 156.

A supply bias cavity 162 is defined between diaphragms 158, 160, middleblock 154 and an outer casing 155. A small capillary hole 164 throughcasing 155 communicates the supply bias cavity with supply pressureinlet 126 so that the supply bias cavity is substantially always underthe supply pressure. Thus, the supply pressure is not only channeled toinput supply port 132, but also enters supply bias cavity 162 viacapillary hole 164. It is desirable that once the supply pressure isestablished in cavity 162, that it not change during the operation ofrelay 48. Momentary fluctuations in the supply pressure can result whensupply port 132 is opened and closed. The capillary hole isolates thesupply bias cavity from pressure transients created when valve plug 138opens or closes supply port 132 in response to load changes. Thiseffectively stabilizes the valve assembly when brief pressurefluctuations occur due to input signal changes thereby resulting inimproved performance.

FIG. 9 illustrates relay 48 in its normal position. When an increasingvariable pressure is coupled to inlet 122, input signal diaphragm 130 isflexed upwardly in FIG. 9 to move bodies 156, 154, 152, exhaust plug140, rod 136 and valve plug 138 also upwardly to unseat the supply port132. Exhaust port 134 remains closed. Supply pressure is thereby coupledfrom inlet 126 through passageways 146, 148 and through open supplyinput port 132 and passageway 150 to actuator outlet 124 and eventuallyto the valve actuator. It may be noted that lower supply bias diaphragm160 contains a greater diaphragm area than the upper supply biasdiaphragm 158. This enables biasing the relay to form an output startpoint commensurate with the input signal based on the given supplypressure.

II. Convertible Current To Pressure Positioner

Reference may now be made to FIGS. 10-18 wherein there is illustrated apreferred embodiment of an electro-pneumatic instrument which is readilyconvertible from a current to pressure positioner to a current topressure transducer and vice versa. The assembled views of FIGS. 10 and11, for instance, illustrate a preferred electro-pneumatic convertibleinstrument 200 providing optimum flexibility in configuration over suchpresently available devices. In particular, the configuration is modularwith respect to several main instrument components, thereby providingthe following advantages:

(1) Enabling a ready conversion of the instrument from a valvepositioner to a pressure transducer in a manner not available with priorinstruments; and

(2) Enabling different types of terminal boxes to be replaceably mountedon the housing for accommodating a variety of field connections andconfigurations.

The electro-pneumatic convertible instrument 200 shown in the assembledviews of FIGS. 10 and 11 is in the form of a valve positioner whichincludes several basic enclosure components in modular form, i.e., ahousing 202, a field terminal box 204 separable from and replaceablymounted on housing 202, and a modular base 206 also replaceably mountedonto housing 202. A removable cover 208 for the instrument enclosure isremovably mounted on modular base 206. A terminal box cover 210 ismounted on field terminal box 204 to protect the contents from theenvironment.

Instrument 200 is in the form of a valve positioner which includes abushing 212 mounted into an elongated cylindrical boss 214 which extendsalong the housing for mounting a potentiometer assembly 216. Elongatedcylindrical boss 214 is formed integrally with housing 202 as a castunit so as to extend along housing back wall 218 (see FIG. 11). Boss 214is hollow and includes an interior pocket 220 which intersects andcommunicates with the hollow interior 222 of housing 202. As can be seenin the exploded view of FIG. 12, potentiometer assembly 216 is insertedwith potentiometer 224 being placed into the interior pocket 220 andwith the potentiometer leads 226 and connector plug 228 extendingthrough interior pocket 220 and into the housing hollow interior 222 toconnect to a printed circuit board 230 mounted within the modular base206. Bushing 212 is then slipped over potentiometer shaft 232 andthreadably engaged into the boss 220 so as to supportably mount thepotentiometer shaft 232 and maintain potentiometer assembly 216 mountedwithin housing 202.

Referring to the assembled view of FIG. 11 and the exploded view of FIG.12, there is illustrated the manner in which the various componentsincluding the potentiometer assembly 216 are mounted to housing 202. Inparticular, field terminal box 204 includes a male threaded end portion233 which is threadably engaged with a corresponding female threadedportion 234 on housing 202. Terminal box 204 includes an interiorportion 236 which leads to a tubular passageway 238 which extends frominterior 236 and at right angles through terminal 204 to the otherterminal end 240 which communicates with the hollow interior 222 ofhousing 202.

A field terminal block 242 is mounted to a printed wiring board 244 andwhich in turn is mounted to a cable harness 246 ending in a connectorplug 248. As is seen from FIG. 12, the terminal block, printed wiringboard, cable harness and connector plug have all been combined into oneassembly. In particular, it may be noted that the cable harness includesradio frequency interference (RFI) filter feedthroughs 250 (see FIG.11).

A significant advantage of this configuration is that it reducesmanufacturing costs required for installing threaded RFI filters intothe housing and then soldering the printed wiring board and terminalblock assembly to the RFI filters. Furthermore, the terminal assemblyshown in FIG. 12 can be more easily replaced and is more reliable ininstallation and operation. In installing the field terminal block 242,and associated cable harness, connector plug 248 is inserted into theinterior 236 and then into tubular passageway 238, continuing beyondterminal end 240 and into the hollow interior 222 of housing 202. Plug248 may then be connected to main printed circuit board 230 on themodular base 206. Within terminal box 204, printed wiring board 244 ismoved against one end of tubular passageway 238 until the board buttsagainst an O-ring 252 and the printed wiring board 244 is maintained inposition by means of screws 254. O-ring 252 acts as a seal to maintainthe housing interior 222 and the main circuit board 230 sealed off fromthe environment. Terminal box cover 210 is then threadably mounted onthe terminal box so as to aid in maintaining the electrical componentsfree from the environment.

Modular base 206 contains a main electrical compartment 256 segregatedon one side of a dividing wall 258 with pneumatic components on theother side of wall 258. In particular, a current to pressure converterdevice such as an I/P nozzle block--flapper unit 260, a pressure relay262, and pressure gauges 264, 266 are all mounted to modular base 206 onone side of dividing wall 258 so as to be physically isolated andsegregated from the electrical components on the other side of wall 258.The electrical components are thus maintained within an explosion proofportion of the instrument enclosure. Also, all of the electrical andpneumatic components, including the pressure gauges are maintainedwithin the instrument enclosure. Cover 208 contains respectivetransparent viewing windows to permit visual reading of gauges 264, 266.

Electrical connections from main printed circuit board 230 to the I/Pconverter are supplied through electrical contacts 268 coupled throughsuitable apertures 270 to the I/P converter 260. Aperture 272 in wall258 is for coupling the supply pressure to the I/P converter 260.Aperture 274 is for coupling the variable pressure from the I/Pconverter to the instrument output as will be described in more detailhereinafter.

FIG. 16 is a front view of the housing face showing the supply pressurecoupled to input port 276 with a passageway 278 connecting the supplypressure to open channels 280 in housing surface 282. Surface 282 alsoincludes another set of open channels 284 which connect to a passageway286 communicating with the instrument output port 288. Accordingly, openchannels 280 and housing surface 282 are associated with the pressure onthe input side or supply pressure side of the system and open channels284 in surface 282 are associated with the variable output pressure sideof the instrument.

FIG. 17 illustrates a rear view of modular base 206, i.e. viewing themodular base from the direction of reference arrow 290 in FIG. 12A withthe electrical compartment 256 removed for ease of illustrating the rearsurface 292 of modular base 206. FIG. 17 shows several passageways whichare provided in modular base 206 to communicate with the fluidpassageways and channels in housing 202 for fluidly interconnecting thevarious components on the instrument. As an example, in FIG. 17,passageway 294 is the relay exhaust passageway, passageway 296communicates supply pressure to the relay, and passageway 298communicates the variable pressure output of the relay and thereforecomprises the instrument output. Passageway 300 communicates with theoutput pressure gauge 264 and passageway 302 communicates with the inputpressure gauge 266. Passageway 304 is coupled to the output pressuresensor 354, and passageway 306 is connected to the I/P converter supplypressure input (see FIG. 14).

As can be seen from the illustrated position of the components in theexploded views of FIGS. 12 and 12A, and with specific reference to FIGS.16 and 17, the input supply pressure on input port 276 which is coupledto passageway 278 and channel 280 communicates with passageway 296 tosupply pressure to relay 262. Relay exhaust passageway 294,communicating through passageway 318 (see FIG. 16), exhausts out therelay exhaust port 308 as shown in FIG. 11. A plastic vent assembly 309prevents dirt and debris from access to relay exhaust port 308.

Intermediate surface 282 of the housing 202 and surface 292 of modularbase 206 there is provided a gasket 310 which can be formed of flexiblerubber material. Gasket 310 covers the open channels 280 and 284 so asto form fluid passageways in the housing 202. Furthermore, gasket 310includes a series of apertures for desirably coupling fluid channelsbetween the modular base and the housing. Note for instance apertures312, 314, 316 which are respectively aligned with passageways 294, 296,298 on modular base 206 as well as with respective passageway 318,channel 280, and 284.

Removable cover 208 includes transparent sections 320, 322 for viewingthe pressure gauges 264, 266 when the cover is closed in position. Ascan be seen from FIG. 12A, cover 208 includes a pair of curved ears 324.Cover 208 is mounted onto modular base 206 by first elevating cover 208until leading edge 326 of each ear 324 is directly facing a respectivecover mounting slot 328 in modular base upper wall 330. This places thecurved ear portions 324 substantially in line with the longitudinal slotso that they can be inserted into the slot until the cover front edge332 abuts the modular base upper wall 330. At this point the cover 208may now be rotated downwardly to the closed position with the curvedears 324 aiding in maintaining the cover in the downward closedposition.

Referring now to FIGS. 13-16, there is illustrated the details ofmounting of the pressure components on modular base 206 and their fluidinterconnections through appropriate passageways. For convenience, inFIG. 13, the input pressure side has been labeled "IN" and the outputpressure side has been labeled "OUT". Referring to FIG. 14, supplypressure through passageway 306 is supplied from input port 276 (seeFIGS. 16 and 17), channels 280, hole 309 in gasket 310 (see FIG. 12),through passageway 306. Passageway 306 interconnects with intersectingpassageway 336 which in turn communicates with passageway 272 whichprovides the input supply pressure to I/P converter 260.

The pressure output side of I/P converter 260 is coupled to passageway274 and then to a vertical passageway 338 in dividing wall 258, thepassageway 338 coupling in turn with the variable pressure input to theinput diaphragm of pressure relay 262 as shown in FIG. 11. Inputpressure gauge 266 is mounted to an upstanding ledge 340 containing apassageway 342 which communicates with passageway 302 (see FIG. 17) soas to couple input supply pressure from channel 280 and input port 276to pressure gauge 266.

With reference to FIG. 15, it can be seen that in a similar manner theoutput pressure gauge 264 is mounted on an upstanding ledge 344. Ledge344 in turn includes passageway 346 which communicates with passageway300 which in turn passes through hole 315 in gasket 310 so as tocommunicate with channel 284 in housing 202. This enables gauge 264 tosense and indicate the output pressure of the instrument.

The instrument variable output pressure developed by pressure relay 262is coupled from the output chamber of pressure relay 262 to passageway348 and through a flame arrester 350 to an intersecting passageway 304,which in turn communicates the pressure through hole 313 on gasket 310to channel 284 on housing 202. A pressure sensor 354 may be provided forsensing the output pressure through passageway 348 as shown on FIG. 14.When this instrument is used as a valve positioner, pressure sensor 354can be used for diagnostic purposes. When the instrument is used as acurrent to pressure transducer, the pressure sensor 354 acts as thefeedback mechanism for the system as will be described more particularlyhereinafter.

Reference may now be made to FIG. 18 wherein there is illustrated aschematic block diagram of instrument 200 with the major componentsshown in a functional block diagram as used for either a valvepositioner or as a pressure transducer. As illustrated with respect tothe preferred embodiment of the invention shown in FIGS. 10-17, there isshown a current to pressure positioner in the form of a valve positionerwhich includes an I/P converter 260 and pressure relay 262 mounted onmodular base 206. Also, housing 202 contains a housing portion, i.e.integral hollow boss 214 and an interior pocket 220 for receiving apotentiometer assembly 216 including a position potentiometer 224. Whenused as a valve positioner, instrument 200 includes a feedback arm 356which includes screw attachment means 358 for attaching the feedback arm356 (see FIGS. 10 and 11) to potentiometer shaft 232 so that the shaft232 is rotated by the feedback arm 356.

With reference to FIG. 18, there is schematically illustrated a fluidcontrol valve 360 and a sliding valve stem actuator 362 with the valveactuator containing a pin 364 connected to move with the valve stemduring linear valve stem movements. Accordingly, as valve stem 362 ismoved vertically up or down as shown by the reference arrows in FIG. 18,pin 364 also moves with the valve stem, and with the pin being coupledto feedback arm 356, the feedback arm is rotated in the mannerillustrated by the rotational reference arrows. Rotation of feedback arm356 rotates the potentiometer shaft 232 and changes the position of thepotentiometer 224 so that the changed position is sensed by positionsensor 366 to couple a variable current to the input of the I/Pconverter 260. Rather than the potentiometer, other feedback elementswith capacitors, inductors, or active elements can be used.

FIG. 11 illustrates the pin 364 maintained in a biased position in aslot 368 in feedback arm 356. A spring clip 370 is biased to maintainpin 364 against the side of slot 368. Accordingly, as the pin 364 ismoved in movements following the valve stem 362, pin 364 also moveslinearly within slot 368 so as to rotate feedback arm 356 and registerthe valve position change into a change in the position of potentiometer224. The signal indicating the change in potentiometer position iscarried by potentiometer leads 226 to the position sensor 366 which ismounted on the main circuit board 230 within electrical compartment 256.The corresponding variable current signal input to the I/P converter 260is carried on input leads 268 from the circuit board 230 throughapertures 270 and into the I/P converter 260.

Accordingly, in the illustrated preferred embodiment of the inventionwhere the instrument is acting as a valve positioner 200, a variablepressure output on output port 288 moves valve stem 362 and pin 364 in acertain manner. This movement is translated by feedback arm 356 into achanged position in potentiometer 224. The changed position is sensed byposition sensor 366 and transformed into a variable current supplied onleads 268 into the I/P converter 260 to provide a variable pressure online 274.

In accordance with one significant advantage of the present invention,the instrument can readily be converted to a pressure transducer. Inorder to accomplish this conversion, electrical compartment 256 may needto be replaced in order to provide a new main circuit board 230. Thatis, it is preferred that the circuit board 230 and the electricalcomponents within electrical compartment 256 are potted within thehollow structure. However, the electrical compartment can readily bechanged by removing four screws 372 to separate modular base 206 fromhousing 202, and then removing plugs 248 and 228 from the main circuitboard 230 before removing electrical compartment 256 and replacing itwith one suitable for use as a pressure transducer. Also, thepotentiometer assembly 16 and bushing 212 could be removed from housingboss 214 and replaced by a suitable plug, or these components can simplybe left in position but not connected with the main circuit board. Inany event, in the current to pressure transducer mode, the feedback ofvariable pressure on output port 288 is coupled through pressure sensor354 to provide a variable current signal supplied on input lead 268 tothe I/P converter 260.

It is understood of course that if the original instrument had been setup as a current to pressure transducer, to convert the instrument to acurrent to pressure positioner would simply have required placement of apotentiometer assembly 216 with a bushing 212 into the interior pocket220 of housing boss 214; changing the main circuit board 230 andpreferably the entire electrical compartment 256 with a new one adaptedfor valve positioner operations; and mounting of feedback arm 356 to thepotentiometer shaft 232 and placing pin 364 in slot 368 for a slidingstem valve operation. It is also understood of course that if a rotaryshaft actuator is used for a fluid valve instead of a sliding stemsituation, then a suitable feedback arm like feedback arm 356 would becoupled to potentiometer shaft 232 and also coupled to a suitable rotarymovement feedback link from the rotary actuator so that movements of thefeedback link generate rotations of potentiometer shaft 232. Other typesof feedback elements, instead of a potentiometer, can be utilized andincorporated into instrument 200 in accordance with the teachingsherein. For example, feedback elements using capacitors, inductors, oractive elements could be used in place of a potentiometer, or incombination.

It is preferred that feedback arm 356 is stabilized with respect tohousing 202 during transit and initial system calibrations, by means ofa pin 374 passing through a suitable aperture in feedback arm 356 asshown for instance in FIG. 10. During operation of the instrument 200the pin 374 is removed.

Referring now to FIGS. 11 and 12A, there is illustrated an improvedpressure relay which utilizes plastic molded structural body componentswhich can be ultrasonically welded together in a manner to clamp thediaphragms to provide the pressure seals so as to eliminate the need formachine screws. In accordance with this aspect of the invention,assembly costs for the pressure relay are drastically reduced and looseparts are minimized. In particular, the plastic body components areformed of a glass filled polyphenylene oxide; the diaphragms are formedof a nitrile with a polyester fabric; and the O-rings are formed ofBuna-N rubber material. In particular, input diaphragm 380, supply biasdiaphragm 382, and feedback diaphragm 384 are maintained spaciallyseparated by the relay body parts and to form the required chambers inthe relay. Exhaust body 386, diaphragm retainer 388, diaphragm spacer390, and supply body 392 are plastic components which maintain thediaphragms separated and form respective relay chambers. The respectiverelay chambers as formed in relay 262 are shown in FIG. 11 as an inputpressure chamber communicating with passageway 338, exhaust chamber 394,supply pressure chamber 396, and output pressure chamber 398.

All of the aforementioned relay components may be ultrasonically weldedtogether using conventional ultrasonic welding equipment and technique.Thus, the main relay body components are readily assembled withultrasonic welding and without the need for any metal screws or othermetal attachments.

The remaining metal components may then be inserted into the relay, suchas valve plug 400, and the conventional supply port and exhaust port. Ametal cap 402 and Belleville springs 404 along with suitable screws 406are used to secure relay 262 to modular base 206. A series of O-rings408 are used on the perimeter of relay 262 in order to seal the variousrelay chambers from each other when installed within modular base 206.Also, within relay 262, supply pressure from chamber 396 is supplied toformed chamber 410 so that the chamber 410 between cap 402 and supplybody 392 is maintained at the supply pressure. Accordingly, thisimproved pneumatic relay also includes the substantially constant supplybias pressure improvement described above in connection with theembodiment of FIGS. 1-9.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

We claim:
 1. An electro-pneumatic convertible instrument readilyconvertible from a pressure transducer to a valve positioner forindicating the position of a valve using a feedback element having ashaft connectable to a valve stem where the feedback element outputcorresponds to the valve stem position, said instrument comprising:anenclosure having a housing defining a hollow interior and including; amodular base having a dividing wall and with electrical and pneumaticcomponents mounted thereon on opposite sides of said dividing wall, saidmodular base removably insertable into said housing and definingrespective electrical and pneumatic compartments within said housing onopposite sides of said dividing wall for segregating said electrical andpneumatic components therein; and said housing including a housingportion adapted for receiving and mounting therein said feedback elementand shaft in converting the instrument to a valve positioner, saidhousing portion having one end thereof opening directly into the housinghollow interior for communicating with said hollow interior to enablesaid feedback element output to be connectable to said electricalcomponents on said modular base and within said electrical compartmentvia said housing portion and said hollow interior.
 2. Anelectro-pneumatic convertible instrument according to claim 1, whereinsaid housing portion includes an elongated cylindrical boss extendingalong said housing.
 3. An electro-pneumatic convertible instrumentaccording to claim 2, wherein said elongated cylindrical boss is formedintegrally with said housing.
 4. An electro-pneumatic convertibleinstrument according to claim 3, wherein said elongated cylindrical bossincludes a pocket interior for receiving said feedback element at onepocket interior end, said pocket interior one end intersecting thehousing hollow interior so the feedback element output is connectable tothe electrical components on the modular base via the housing portionand the hollow interior.
 5. An electro-pneumatic convertible instrumentaccording to claim 4, including a bushing threadably mountable on saidelongated cylindrical boss at said pocket interior other end forsupportably mounting said feedback element shaft.
 6. Anelectro-pneumatic convertible instrument according to claim 5, whereinsaid feedback element includes a potentiometer.
 7. An electro-pneumaticconvertible instrument according to claim 1, including an electricalterminal box, means for replaceably mounting said electrical terminalbox on said housing, and passageway means through said electricalterminal box and said housing enabling electrical connections betweensaid terminal box and said electrical components on said modular basevia said passageway means and said housing hollow interior.
 8. Anelectro-pneumatic convertible instrument according to claim 7, includingan electrical terminal board replaceably mounted in said terminal box,and a removable cover for said terminal box.
 9. An electro-pneumaticconvertible instrument according to claim 8, including a cable harnessconnected to said electrical terminal board and extending through saidpassageway means and said housing hollow interior for connection to saidelectrical components on said modular base, said terminal board andcable harness being a unitary assembly and replaceable to accommodatecorresponding desired functions, including one or more analog, digitalcommunication or data protocols functions.
 10. An electro-pneumaticconvertible instrument according to claim 9, wherein said cable harnessincludes radio frequency interference filters in said unitary assembly.11. An electro-pneumatic convertible instrument according to claim 1,including screw means for screw mounting said modular base to saidhousing, and a removable cover enclosing said electrical and pneumaticcomponents on said enclosure, in a closed position, and removable toenable ready access to said segregated pneumatic components within saidpneumatic compartment.
 12. An electro-pneumatic convertible instrumentaccording to claim 11, including self-contained means associated withsaid modular base and said removable cover enabling removable mountingof said cover on said modular base without any other mounting structure.13. An electro-pneumatic convertible instrument according to claim 12,wherein said self-contained means includes at least one slot on saidmodular base and at least one projecting curved portion on said cover,said projecting curved portion insertable into said slot during mountingof said cover on said modular base and said curved portion enabling saidcover to rotate to a closed position while maintaining said cover onsaid modular base.
 14. An electro-pneumatic convertible instrumentaccording to claim 13, wherein said self-contained means includes a pairof said slots on opposite sides of said modular base and a pair of saidprojecting curved portions respectively associated therewith.
 15. Anelectro-pneumatic convertible instrument according to claim 1, includinga pneumatic relay mounted to said modular base, including plastic relaybody components and rubber diaphragms, and ultrasonic weld means weldingtogether said plastic relay body components and said rubber diaphragms.16. An electro-pneumatic converter comprising:an enclosure having ahousing defining a hollow interior ending in a housing mounting surface,said housing including an inlet pressure port and an outlet pressureport; said housing mounting surface having respective channels thereincommunicating with said inlet pressure port and said outlet pressureport, respectively; a modular base having a dividing wall and withelectro-pneumatic components mounted thereon on opposite sides of saiddividing wall, said modular base removably insertable into said housinghollow interior and defining respective electrical and pneumaticcompartments within said housing hollow interior on opposite sides ofsaid dividing wall for segregating said electrical and pneumaticcomponents therein, said modular base including a modular base mountingsurface oppositely disposed and immediately adjacent said housingmounting surface; said modular base mounting surface having modular basefluid passageways communicating with said electro-pneumatic components;and a gasket intermediate and immediately adjacent said housing mountingsurface and said modular base mounting surface, said gasket coveringsaid channels to define housing fluid passageways, and includingapertures for communicating said housing fluid passageways to saidmodular base fluid passageways.